I. Field of the Invention
The present invention relates generally to push-to-talk communication systems and more particularly to a method and apparatus for providing fair access to members of a push-to-talk communication system in which the members experience differing signaling delays.
II. Description of the Related Art
Point-to-multipoint communication systems have been used for many years to provide communications generally between a central location and multiple users of the system. For example, dispatch systems using Land Mobile Radios (LMRs) have been used in trucks, taxis, buses, and other vehicles in order to communicate scheduling information between a central dispatch center and one or more corresponding fleet vehicles. Communications may be directed at a specific vehicle in the fleet or to all vehicles simultaneously.
Another example of a point-to-multipoint communication system is a push-to-talk communication system. Such a system allows a group of individuals, each having a wireless communication device, to communicate with other members of the group. Typically, a push-to-talk system relies on a single frequency, or dedicated channel, over which communications are received by the wireless communication devices. Only one member may transmit information to the other members at a time. However, all members can listen to a dedicated broadcast channel to receive communications from the single member who is transmitting. Members desiring to communicate with other members of the system typically depress a push-to-talk button on their respective communication devices which allows them sole access to the dedicated channel. Hence, these systems are known as push-to-talk communication systems.
Push-to-talk systems are typically used in outdoor settings where a group of people, or members, require communications with each other in a "point-to-multipoint" fashion. Examples of push-to-talk system uses include workgroup communications, security communications, construction site communication, and localized military communications. The group of people requiring communications with each other is commonly known as a "net," each member of the net sometimes referred to as a "net member," or simply a "member."
In a typical push-to-talk system, a dedicated channel, sometimes referred to as a broadcast channel, is used to transmit communications from one member to multiple other members of the net simultaneously. The broadcast channel may comprise a single channel or frequency, or a group of individual channels managed by a controller to imitate the single channel. In either case, only one member may transmit voice and/or data communications to the other member users at any given time. If another member attempts to transmit voice and/or data over the broadcast channel while another member is transmitting, interference between the two competing communications will occur, resulting in non-intelligible voice and/or data being received by the other net members.
To prevent interference between members, many push-to-talk systems use an arbitration device to limit access to the broadcast channel to only one net member at any given time. Typically, the arbitration device is located at a central facility, base station, or other communication facility where communications between net members pass. The arbitration device typically comprises a digital computer which monitors transmissions from members for a transmission request message. The transmission request message is typically generated upon a net member depressing a push-to-talk button, located on the wireless communication device. The transmission request is transmitted from the wireless communication device to the arbitration device prior to a net member commencing transmissions.
In practice, members generally listen to communications over the dedicated channel and attempt to transmit when there is a moment of silence in the communications, for example, when a net member has finished transmitting. At that time, the member wishing to transmit generally presses and holds a push-to-talk button located on his or her communication device. If the requesting member is granted transmission privileges by the arbitration device, he or she may begin transmitting communications to other members belonging to the broadcast communication system.
Generally, the arbitration device will grant transmission privileges to a requesting member only if no other member is presently using the broadcast channel. In other systems, a priority scheme is used to decide who is given transmission privileges when another member currently possesses the transmission privilege.
In another situation, two or more transmission requests from two or more communication devices are received by the arbitration device at or substantially the same time. In this case, the arbitration device decides which of the requests is granted transmission privileges, assuming that no other member is currently transmitting.
One problem with such an arbitration arrangement is that members who experience large signaling delays between when a transmission request is generated and when the transmission request is received by the arbitration device will have a smaller chance of being granted the transmission privilege. Such a problem might be common for a member who is operating a satellite communication device, for example. In that case, such a member may try to gain access to the communication system by pressing a push-to-talk button on his or her satellite communication device after a broadcast by another member has ceased. However, by the time the transmission request is received by the arbitration device, other members who are operating within a closer proximity to the arbitration device, generally using a terrestrial communication system, will most likely have their transmission requests received at an earlier time than the satellite member's request. Because many arbitration devices award transmission privileges on a "first come, first served" basis, the satellite member may not be able to compete fairly with other members for the opportunity to speak.
What is needed is an arbitration device that will allow members who experience large signaling delays in transmitting transmission requests to improve their chances of obtaining transmission privileges.